Abstract
Refractive indices of in-plane and out-of-plane directions were measured for a poly(amic acid) (PAA) synthesized from biphenyltetracarboxylic dianhydride and p-phenylenediamine and PAA synthesized from biphenyltetracarboxylic dianhydride and p,p′-diaminodiphenylether. Depth dependence of in-plane orientation was observed for both PAAs. The degree of in-plane orientation is larger around the air/film interface than the film/substrate interface. Factors which contribute to increase in average refractive index are solvent evaporation, thermal imidization and dense packing during heating. Solvent evaporation is dominant for curing at temperatures below 100°C, thermal imidization is dominant for curing at temperatures from 100°C to 200°C and change in packing becomes important for curing at temperatures above 200°C.
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